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Summer ice in the Antarctic is melting 10 times quicker than it was 600 years ago, with the most rapid melt occurring in the last 50 years, a joint Australian-British study showed yesterday.

A research team from the Australian National University and the British Antarctic Survey drilled a 364-metre-long ice core from James Ross Island in the continent's north to measure past temperatures in the area.

Visible layers in the ice core indicated periods when summer snow on the ice cap thawed and then refroze.

By measuring the thickness of these melt layers, the scientists were able to examine how the history of melting compared with changes in temperature at the ice core site over the last 1,000 years.

"We found that the coolest conditions on the Antarctic peninsula and the lowest amount of summer melt occurred around 600 years ago," said lead author Dr Nerilie Abram of the ANU Research School of Earth Sciences.

"Temperatures then were around 1.6 degrees Celsius lower than those recorded in the late 20th century and the amount of annual snowfall that melted and refroze was about 0.5 per cent.

"Today, we see almost 10 times as much of the annual snowfall melting each year.

"While temperatures at this site increased gradually in phases over many hundreds of years, most of the intensification of melting has happened since the mid-20th century," she added.

The research, published in the journal Nature Geoscience, is only the second reconstruction of past ice melt on Antarctica.

Abram said it helped scientists gain more accurate projections about the direct and indirect contribution of Antarctica's ice shelves and glaciers to global sea level rise.

"What it means is that the Antarctic peninsula has warmed to a level where even small increases in temperature can now lead to a big increase in summer ice melt," she said.

This article appeared in the South China Morning Post print edition as: